Conventional spear guns may be classified according to two general types, with one being a pneumatic spear gun, which utilizes an air-driven piston or a CO.sub.2 cartridge to drive the spear shaft down a rifle-like barrel, and the other being a rubber-powered or sling-type spear gun, in which one or more elastic bands propel the spear shaft.
Inasmuch as the water is highly resistant to the progress of a spear shaft for any great distance, high muzzle velocity is necessary to propel the spear shaft with any great force.
The pneumatic type of spear gun using a pumping arrangement is advantageous in that it is a relatively accurate device, allowing accurate aiming of the spear shaft. However, it is disadvantageous inasmuch as the power to drive the spear shaft is limited by the physical strength of the user of the gun inasmuch as during loading, the air is further compressed and the piston set by the diver himself.
The only way to increase the power of this type of pneumatic spear gun is to increase the initial pressure of the compressed air. If such initial pressure were to be too great, however, the diver would not be able to overcome it during each loading. Thus, each pneumatic spear gun necessarily has a limit to the maximum power output thereof, which also is directly dependent upon the diver's strength.
The type of pneumatic spear gun using a CO.sub.2 cartridge does not require pumping, and the user can aim down the barrel of the gun, but it has a very short range. Furthermore, the gas seal often leaks, maintenance and cost is high, and popularity is low.
In comparison with these types of pneumatic spear guns, the rubber-powered spear gun has the considerable advantage of a greater power output, and therefore, the possibility of greater spear shaft range. However, one disadvantage is the offset aiming accuracy associated with some embodiments of the band powered gun.
With conventional band powered spear guns, a definite amount of strength is usually involved, and one way of cocking the gun is to place the gun stock against the user's stomach or chest and to pull back with both arms on the elastic band that is then fitted in a notch in the spear shaft or harpoon. To assist in cocking the gun, the butt end of the gun stock is sometimes provided with a soft packing or the like.
Conventional band powered guns with the usual type of cocking arrangement provide no adjustment of shaft velocity, and a maximum arm strength effort to load such a gun must necessarily take place prior to firing the spear shaft in the direction of the intended target.
It is an important object of this invention to utilize a cocking arrangement of a type such that the power band of the gun can be stretched to a desired extent by almost anyone, irrespective of age or reasonable physical strength, with such cocking able to be accomplished while the user is swimming on the surface, under water, or in open air, as may be desired by the user.
Another object of this invention is to provide a cocking procedure wherein the center portion of the power band is drawn rearwardly by rearward movement of the spear shaft, and after the power band has been suitably tensioned, the spear shaft is momentarily immobilized by the user firmly gripping the trigger member, with the arrangement being such that successive stretchings of the band can be accomplished, to provide a variety of power output possibilities that can be maintained by suitable pressure applied to the trigger of the device by the user. As should be apparent, more potential energy is able to be stored in the power band in accordance with this advantageous procedure than could be accomplished using ordinary procedures.